Lighting systems, particularly in commercial settings, are subject to a number of strict functional requirements set by various standard setting organizations. Among these is the requirement that emergency lighting be provided in the event of a loss of building power. These mandated emergency power systems must provide backup lighting for a predetermined period of time, must be tamper, fire, flood and earthquake resistant, and must meet certain other functional requirements. Conventionally, emergency lighting systems are provided as self-contained units installed in light fixtures, which include batteries charged by a dedicated A/C power line.
The promulgation of IEEE standards for power-over-Ethernet (“POE”), combined with the ubiquity of RJ45 Ethernet cabling in modern business and residential buildings, provides alternative means for building lighting. There are at present two ratified IEEE standards for POE: IEEE 802.3af and IEEE 802.3at. An Ethernet port operating in accordance with the IEEE 802.3af standard is capable of supplying 12.95 Watts to powered devices (“PDs”) over a POE link. IEEE 802.3at defines the POE+ standard, which enables the delivery of up to 25.5 W over a POE link. Current efforts are underway to promulgate more advanced POE standards (e.g., POE+ and POE++), which will specify equipment capable of supplying up to 90 W over a POE link.
Realizing a POE link over the physical connections of Cat5+ Ethernet cable is done according to one of two alternatives, illustrated schematically in FIG. 1. As can be seen in FIG. 1, an RJ45 Ethernet cable 105 carries 8 conductors grouped as 4 twisted pairs (110a,b and 115a,b), with two twisted pairs (e.g., 110, 115) forming a communication link for a first port (transmit and receive), and with the two remaining twisted pairs available as spares (e.g., 115a,b). In Alternative A, a DC voltage is supplied over data lines, across center taps on internal signal coupling transformers (120 a,b) connected across the pair of conductors on each of the transmit and receive twisted pairs. The DC voltage is then supplied from the center taps of another pair of transformers (125 a,b) across the receive-side twisted pairs for the transmit and receive lines. This DC voltage is supplied to a powered device 130 on the receive end of the link. In Alternative B of the POE standard, DC voltage is supplied through the unused or spare twisted pairs. Newer and proposed POE standards provide more power and faster data using all 8 conductors. These methods require 4 Data transformers, where Power is imposed on all pairs.
In recent years, with the declining cost and increased efficiency of light emitting diodes (“LEDs”), LED lighting has begun to replace fluorescent lighting in commercial settings. FIG. 2 is a schematic representation of a conventional LED lighting installation powered by a POE link, or more precisely, an Ethernet cable referred to under the POE standards as a Port Data Link Segment. 48V DC nominal is supplied over the link by power sourcing equipment (“PSE”) 205 (e.g., a POE switch, hub or midspan injector). The power is superimposed on data transmission wire pairs of an Ethernet link segment (e.g., 210a, b) carried on a CATnx (e.g., Cat 5+) cable. The link segments (210a,b) supply power to a Powered Device (PD), for example, POE luminaire Lighting LED Driver 220, where the power is intelligently extracted (i.e., separated from the data) at the PD. Power extraction occurs at a POE Lighting LED Driver 220, which appears to the PSE as any conventional PSE operating according to the POE standards. Power is then delivered by the driver 220 to LED lamps 225. In certain conventional implementations, driver 220 and LED lamps 225 are co-located in an LED luminaire 215, which is installed, for example at a ceiling light fixture.
In a typical AC Power System, certain luminaires (i.e., light fixtures) are designated as also emergency luminaires, which by code and accepted building practice must maintain illumination upon a loss of AC power. Luminaires are complete with all the necessary luminaire components; e.g., light sources (lamps, such as LEDs), a ballast or lamp power supply such as an LED driver), etc. If a luminaire is to also act as an emergency luminaire, it is outfitted with additional hardware enabling it to drive all or a portion of the light sources (i.e., lamps) for emergency illumination in emergency-mode operation—a condition triggered by the loss AC power. Thus, the existing lamps in these luminaires are used both for normal lighting when AC power is supplied, and also for illumination in emergency-mode operation when normal AC power fails.